The aim of this study was to assess in vitro meiosis resumption and nuclear maturation of Rattus norvegicus oocytes after vitrification with different cryoprotective solutions. Cumulus-oocyte complexes (COCs) were exposed to an equilibration solution for 4 min placed in cryoprotective solutions for 1 min and vitrified in open pulled straws. Cryoprotective solutions were prepared with 15% ethylene glycol + 15% dimethyl sulfoxide + 0.5 M sucrose and different supplements, to form the following groups: G1, 20% fetal bovine serum in modified phosphate-buffered saline (mPBS); G2, 0.4% bovine serum albumine in mPBS; G3, 1% hyaluronic acid in mPBS; and G4, 0.4% polyvinyl alcohol in mPBS. Seven days after vitrification, the COCs from G1 to G4 were warmed and in vitro matured for 30 h along with the control group. Hoechst staining was performed to assess meiosis resumption and nuclear maturation rates. Control group showed higher meiosis resumption (77.88%) and nuclear maturation rates (55.75%) compared to all vitrified groups. Among the vitrified COCs, G3 showed the highest meiosis resumption and nuclear maturation rates (G1, 26.5 and 15.38%; G2, 22.12 and 11.54%; G3, 34.55 and 20%; G4, 20.17 and 9.24%). Supplementation of the vitrification solution with 1% hyaluronic acid provided better results, compared to the other supplements. Hyaluronic acid can be useful to vitrify rat COCs associated with other cryoprotectant agents.
Keywords: Hyaluronic acid; Maturation; Oocyte; Rat; Vitrification.